1. Field of the Invention
The present invention relates to an optical writing device, an image forming apparatus, and a method of controlling the optical writing device.
2. Description of the Related Art
Recently, digitization of information tends to be promoted, and image forming apparatuses, like printers and facsimile machines used for output of digitized information and scanners used for digitization of documents, have become essential apparatuses. Many image forming apparatuses include imaging functions, image forming functions, communication functions, and the like, to be configured as multifunction peripherals that are usable as printers, facsimile machines, scanners, and copiers.
Of these image forming apparatuses, electrophotographic image forming apparatuses are widely used as image forming apparatuses used for output of digitized documents. An electrophotographic image forming apparatus forms an electrostatic latent image on a photosensitive element by exposing a photosensitive element, and develops the electrostatic latent image into a toner image using a developer such as toner, and transfers the toner image onto a sheet of paper to output the sheet of paper.
There are several types of optical writing device which exposes a photoreceptor to an optical beam in an electrophotographic image forming apparatus: a laser diode (LD) raster optical system type and a light emitting diode (LED) writing type. The LD raster optical system type of optical writing device includes a light source, which emits a beam to expose a photoreceptor, and a deflector, such as a polygon scanner, for deflecting the emitted beam to scan the entire surface of the photoreceptor; the LED writing type of optical writing device includes an LED array (LEDA) head. In such an optical writing device, the LD raster optical system type has an error due to skew, positional shift, etc. of an f-theta lens and a reflecting mirror; the LED writing type has skew, an installation error, etc. of the LEDA head.
The LED writing type of optical writing device forms an electrostatic latent image by exposing a photosensitive drum with the use of an LEDA as described above. The on/off of light emission of each of LED elements included in the LEDA is controlled depending on an image to be formed and output. Therefore, when pixel information indicating the on/off of light emission of each of the LED elements is generated on the basis of information of the image to be formed and output, a control unit for controlling the LEDA stores the generated pixel information in a line memory with respect to each main scanning line, and then controls the on/off of light emission of the LEDA in accordance with the predetermined control timing.
Furthermore, there have been known methods to correct misregistration of an image in a sub-scanning direction or skew due to an assembly error of an LEDA or a photosensitive drum by controlling the read of pixel information stored in a line memory (for example, see Japanese Patent Application Laid-open No. 2007-106126).
Conventionally, such corrections of misregistration and skew as described above are made by installing different line memories; therefore, it is necessary to install a line memory with respect to each function, and this causes an increase in cost of an optical writing device including an LEDA.
There is a need to reduce the number of line memories installed in an optical writing device and the cost of the device.